1. Field of the Invention
The present invention relates to a default device of an actuator for a variable lift valve operating mechanism in which in the event of failure of the actuator that rotatably drives a control shaft of a variable lift valve operating mechanism capable of varying valve lift of an engine valve of an internal combustion engine, the control shaft is urged in one direction by an urging member of a default mechanism to prevent the valve lift from being a predetermined value or lower.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2000-227010 discloses a variable lift valve operating device of an internal combustion engine in which a control shaft is rotated by an electric motor via a drive gear and a driven gear to vary a position of a pivot of a rocker arm, and valve lift or valve timing of an intake valve is variably controlled according to an engine operation state.
The variable lift valve operating device includes a default mechanism for stopping the control shaft in an intermediate position between a maximum valve lift position and a minimum valve lift position so as to continue an operation of the internal combustion engine without any problems in the event of failure of the electric motor when the control shaft is placed in the maximum valve lift position or the minimum valve lift position. The default mechanism is placed between an end of the control shaft and the driven gear relatively rotatably supported on an outer periphery of the end. The default mechanism is adapted to return the control shaft and the driven gear to a position where intermediate valve lift between the maximum valve lift and the minimum valve lift can be obtained by a resilient force of a coil spring housed in the driven gear in the event of failure of the electric motor, and relatively nonrotatably lock the control shaft and the driven gear with a lock pin.
The default mechanism described in Japanese Patent Application Laid-Open No. 2000-227010 is placed between the control shaft and the driven gear which are coaxially placed. In order to obtain a sufficient default load with the resilient force of the coil spring, there is a need for increasing the size of the coil spring or increasing the diameter of the driven gear that houses the coil spring, in either case the size of the default mechanism disadvantageously increases.